title: Activity of the hypoxia-activated prodrug, TH-302, in preclinical human acute myeloid leukemia models.
abstract: OBJECTIVE
  Acute myeloid leukemia (AML) is an aggressive hematologic neoplasm. Recent evidence has shown the bone marrow microenvironment in patients with AML to be intrinsically hypoxic. Adaptive cellular responses by leukemia cells to survive under low oxygenation also confer chemoresistance. We therefore asked whether therapeutic exploitation of marrow hypoxia via the hypoxia-activated nitrogen mustard prodrug, TH-302, could effectively inhibit AML growth.
  
  
  METHODS
  We assessed the effects of hypoxia and TH-302 on human AML cells, primary samples, and systemic xenograft models.
  
  
  RESULTS
  We observed that human AML cells and primary AML colonies cultured under chronic hypoxia (1% O2, 72 hours) exhibited reduced sensitivity to cytarabine-induced apoptosis as compared with normoxic controls. TH-302 treatment resulted in dose- and hypoxia-dependent apoptosis and cell death in diverse AML cells. TH-302 preferentially decreased proliferation, reduced HIF-1α expression, induced cell-cycle arrest, and enhanced double-stranded DNA breaks in hypoxic AML cells. Hypoxia-induced reactive oxygen species by AML cells were also diminished. In systemic human AML xenografts (HEL, HL60), TH-302 [50 mg/kg intraperitoneally (i.p.) 5 times per week] inhibited disease progression and prolonged overall survival. TH-302 treatment reduced the number of hypoxic cells within leukemic bone marrows and was not associated with hematologic toxicities in nonleukemic or leukemic mice. Later initiation of TH-302 treatment in advanced AML disease was as effective as earlier TH-302 treatment in xenograft models.
  
  
  CONCLUSIONS
  Our results establish the preclinical activity of TH-302 in AML and provide the rationale for further clinical studies of this and other hypoxia-activated agents for leukemia therapy.
authors.affiliation: Authors' Affiliations: Departments of Medicine, Immunology, Roswell Park Cancer Institute, Buffalo, New York; and Threshold Pharmaceuticals Inc, South San Francisco, California.
authors.forename: Scott
authors.initials: S
authors.lastname: Portwood
authors.forename: Deepika
authors.initials: D
authors.lastname: Lal
authors.forename: Yung-Chun
authors.initials: YC
authors.lastname: Hsu
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Vargas
authors.forename: Megan K
authors.initials: MK
authors.lastname: Johnson
authors.forename: Meir
authors.initials: M
authors.lastname: Wetzler
authors.forename: Charles P
authors.initials: CP
authors.lastname: Hart
authors.forename: Eunice S
authors.initials: ES
authors.lastname: Wang
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis; D001853:Bone Marrow / Q000378:metabolism / Q000473:pathology; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D053938:DNA Fragmentation; D005260:Female; D018922:HL-60 Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy* / Q000473:pathology; D051379:Mice; D016513:Mice, SCID; D009593:Nitroimidazoles / Q000494:pharmacology* / Q000627:therapeutic use; D010752:Phosphoramide Mustards / Q000494:pharmacology* / Q000627:therapeutic use; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D017382:Reactive Oxygen Species / Q000378:metabolism; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; C468783:H2AX protein, human; C497442:HIF1A protein, human; D006657:Histones; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009593:Nitroimidazoles; D010752:Phosphoramide Mustards; D017382:Reactive Oxygen Species; C552526:TH 302